There is an increasing demand for low cost, high volume solution of miniature lenses in an ever increasing number of applications, such as in mobile phones, laptops, web cameras, etc. The popular use of cameras in mobile phones alone provides a market for millions of lenses. Additionally there is a growing demand in the market with respect to resolution of such miniature cameras and thereby an increasing need for adjustable lenses providing advanced functionalities, such as fast auto focus or zoom. This invention relates to solutions for problems that arise in search for adjustable lenses having advanced functionalities.
US 20110038625 discloses a rather complex adaptive lens comprising at least an actuator and a lens, the lens being mechanically coupled to the actuator so that energization of the actuator adjusts a focal point of the lens. The actuator may comprise a multilayer stack of electromechanical polymer (EMP) layers, having electrodes configured to apply an electric field across each EMP layer. The actuator may be operable to move and/or deform a lens, so as to adjust the focus properties of the lens. In some examples, the actuator has an annular shape, supporting a lens within the inner radius of the annulus. In other examples, the actuator may be mechanically coupled to a surface of a deformable lens, either directly or through another element of a lens structure. This adjustable lens assembly seems to be rather complex in that it comprises several moving parts consisting of different materials. The lens body or lens structure itself is said to be prepared by molding using a mold, where it can be cured. When cured, the lens structure is removed from the mold and an actuator is mounted on one or both sides of the lens structure.
Like in US 20110038625, it is quite common within fabrication of polymer lenses to use replica molding either with thermal or UV curing, where the lens body is prepared in one piece and thereafter removed from the mould for mounting into the desired device, often by use of some sort of fixing agent. This is considered to be an inconvenient and labor-intensive technical method which is considered disadvantageous for fast production of millions of tuneable miniaturized lenses.
Several technical problems are encountered by using a fixing agent or adhesive, such as glue, when one have to introduce a new material into the lens assembly, while maintaining the optical and mechanical quality of the lens assembly. By way of example the fixing agent must have a refractive index matching the refracting index of the lens to avoid optical disturbances. Furthermore the fixing agent must be compatible with the other parts and materials of the lens assembly, both chemically, optically and mechanically. It is also necessary to retain the elasticity and flexibility of the lens body and other parts of the adjustable lens assembly, and accordingly the fixing agent must be just as soft and flexible as the other flexible parts of the assembly. If such requirements are not met, tensions will rise between the different parts of a lens assembly, e.g. between a fixing agent, a glass surface, an actuator and/or a lens body, i.e. between all parts having an undesired stiffness.
Still another problem faced by using a fixing agent is the thermal expansion of a further component as the fixing agent will typically have a different coefficient of thermal expansion than the other components of the lens assembly when exposed to different temperatures giving rise to tensions in the lens assembly. It is well known that that especially hybrid materials, built up of materials with large differences in thermal expansion, such as glass, silicon, polymers and metal, will face problems both during operation and during manufacturing (wherein high temperatures are final device) due to large differences in the thermal expansion of the different materials. Accordingly, introduction of even further elements will increase the problem. In this respect it can be mentioned that WO 2010/005315 discloses a method and arrangement for reducing thermal effects in compact adjustable optical lenses.
If a further component, such as a fixing agent, is to be introduced, this will also require further process steps making the process even more complex and probably slower. Additionally, the hardening and curing time must be controlled to obtain a successful lens assembly having the desired optical and mechanical properties.
Accordingly, there is a need FOR a lens assembly process wherein the use of fixing agent(s) is/are avoided.
Different other types of improved adjustable lenses have been developed and described for example in the following patent applications: NO20064271, WO 2010/005315, WO 2008/100154 and WO 2008/044937.
The compact adjustable lens according to WO 2010/005315 is considered to be an especially interesting lens. This adjustable optical lens comprises a deformable lens body confined in a cavity bounded by a flexible glass surface supported by rigid sidewalls and an attached transparent bottom plate. Furthermore, there is an opening between the sidewalls and the edges of the transparent bottom plate and a corresponding opening around the lens body and the sidewalls. Additionally actuators are arranged on the flexible glass surface to deform the lens body, thereby enabling adjustments of focal length.
The above mentioned lens design requires a flexible polymer that is partially surrounded by air (no physical contact with the sidewalls of the cavity). A further problem faced when manufacturing such a lens is how to shape the deformable polymer in such a (flat) cylindrical shape.
There are many issues to be solved associated with adjustable optical lenses and their manufacturing wherein a soft polymer is deformed by an actuator layer structure that is located adjacent to a surface of the soft polymer constituting the lens body. Especially, the manufactured lens must satisfy certain strict requirements with respect to optical and mechanical properties. First of all the lens body must be uniform in all directions, i.e. isotropic, as any kind of anisotropy with respect to optical properties will result in a lens with different optical properties in different directions of the lens body. Thus, an isotropic lens body will have homogeneous optical properties, such as refraction and transmittance, throughout the whole lens body. Anisotropy, such as birefringence, is highly undesirable, as it leads to poor optical quality in a captured image. Thus, the absence of structural defects in the lens body is appreciated. Furthermore the lens body must be clear and highly transparent, allowing light to be transmitted through the lens. All kinds of impurities, including air bubbles, having a different refractive index compared to the lens material, must be avoided.
It is also important that the optical and mechanical properties remain relatively stable at the temperatures the device, e.g. a camera, will be exposed to during operation. If changes occur over a temperature range, it is important that there are no abrupt, irreversible or unpredictable changes. Thus, not only must the lens including the polymer body withstand high temperatures during manufacturing but it must also function at much lower temperatures as the lens may be operated at temperatures ranging from −25 to 80° C., or wider.
Further problems to be solved are the difficulties related to mass production of such adjustable lens assemblies such as the speed of the process. In order to enable the mass production of millions of lenses per year, at prices low enough to be available for relatively low cost electronic products, quite strict limitations are put on the manufacturing processes.
Hence, a transparent optical device element comprising a deformable lens body having an improved mechanical stability would be advantageous, and in particular a deformable lens body having a high refractive index, an optimal degree of stiffness and sheer modulus would be advantageous.